Provided by Justin Glisan, Ph.D., State Climatologist, Iowa Department of Agriculture and Land Stewardship
Unseasonably cool temperatures persisted across Iowa during the reporting period with negative departures of up to eight degrees observed in the state’s southeast corner; the statewide average temperature was 52.7 degrees, 7.4 degrees below normal. Late spring showers and thunderstorms also developed over much of Iowa, with the highest rain totals occurring in the southeast, though for this time of year, drier than normal conditions were reported at all Iowa observing stations.
As the potent low pressure system pushed east of Iowa, partly cloudy skies prevailed through Sunday (9th) with afternoon highs in the upper 50s and low 60s under light, variable winds. Overnight temperatures dipped into the 40s as a weak disturbance moved through eastern Iowa, shifting winds to a northeasterly direction on that side of the state. Rain showers developed over eastern Iowa early on Monday (10th) with very light totals where rain fell. As the patten cleared and a dome of high pressure took hold over the Midwest, skies cleared with light northerly winds overnight into Tuesday (11th) morning. Lack of cloud cover and a colder air mass allowed temperatures to fall below freezing in portions of northern Iowa, while mid 40s were observed across southern Iowa; the statewide average low was 36 degrees, 11 degrees below normal. Mostly sunny skies remained across Iowa through the day with highs in the upper 50s and lower 60s, cooler than what is expected for mid-May. As the stars became visible, calm conditions allowed temperatures to drop back into the upper 30s and low 40s with light variable winds. At sunrise on Wednesday (12th), conditions remained calm and clear with a light southerly wind. Afternoon highs warmed into the mid 60s statewide, leading to a pleasant day for Iowans.
Light southerly winds built in overnight into Thursday (13th) with temperatures staying in the upper 30s and low 40s. Sunny skies allowed temperatures to climb into the mid to upper 60s. Clouds increased through early morning Friday (14th) in advance a low pressure center over the Dakotas, producing showers in western Iowa during late morning. The area of rainfall pushed into central Iowa and persisted across eastern Iowa into the evening. Scattered showers reformed over Iowa’s eastern half into Saturday (15th) with totals reported at 7:00 am highest from central Iowa into the southeast corner; a rain gauge in Prole (Warren County) measured 1.16 inches. General amounts where showers persisted ranged from 0.25 inch to 0.75 inch; the statewide average was 0.21 inch. A secondary disturbance moving through northern Iowa along with warm daytime highs forced showers and thunderstorms to fire during the afternoon and evening hours. Some storms were strong with heavy downpours; a severe thunderstorm produced large hail, with a diameter of 1.75 inches, in Fayette (Fayette County). The line of thunderstorms dissipated into the evening hours with foggy conditions observed overnight, given higher dew points and low temperatures in the 50s. Rain totals reported on Sunday (16th) morning were mostly a few tenths of an inch, though several stations reported over 0.50 inch; Keokuk Lock and Dam (Lee County) measured 1.01 inches while Grundy Center (Grundy County) observed 1.40 inches.
Weekly precipitation totals ranged from no rainfall at a handful of northern Iowa stations to 1.49 inches in Grundy Center. The statewide weekly average precipitation was 0.37 inch while the normal is 0.79 inch. Sioux City Airport (Woodbury County) observed the week’s high temperature of 79 degrees on the 15th, seven degrees above normal. Estherville Municipal Airport (Clayton County) reported the week’s low temperature of 26 degrees on the 11th, 18 degrees below normal. Four-inch soil temperatures were in the upper 50s southeast to near 60 northwest as of Sunday.